Process for obtaining a high contrast silver halide photographic image

ABSTRACT

PROCESS FOR OBTAINING AHIGH CONTRAST SILVER HALIDE PHOTOGRAPHIC IMAGE, WHEREIN, AFTER IMAGEWISE EXPOSURE TO LIGHT, A LIGHT-SENSITIVE SILVER HALIDE PHOTOGRAPHIC MATERIAL HAVING A SILVER HALIDE EMULSION LAYER IS TREATED WITH A LITHTYPE ALKALI DEVELOPER CONTAINING HYDROQUINONE AS A DEVELOPING AGENT, SAID DEVELOPER FURTHER COMPRISING A THIOCYANATE COMPOUND CAPABLE OF LIBERATING THIOCYANATE IONAND NOT MORE THAN 0.004 MOLE OF POTASSIUM BROMIDE PER LITER OF THE DEVELOPER.

United States Patent 3,799,780 PROCESS FOR OBTAINING A HIGH CONTRASTSILVER HALIDE PHOTOGRAPHIC IMAGE Tsuneo Suga, Tokyo, Japan, assignor toKonishiroku Photo Industry Co., Ltd.

No Drawing. Filed May 10, 1972, Ser. No. 252,014 Claims priority,application Japan, May 12, 1971, 46/ 31,141 Int. Cl. G03c 5/30 US. Cl.96-66 R 7 Claims ABSTRACT OF THE DISCLOSURE Process for obtaining a highcontrast silver halide photographic image, wherein, after imagewiseexposure to light, a light-sensitive silver halide photographic materialhaving a silver halide emulsion layer is treated with a lithtype alkalideveloper containing hydroquinone as a developing agent, said developerfurther comprising a thiocyanate compound capable of liberatingthiocyanate ion and not more than 0.004 mole of potassium bromide perliter of the developer.

This invention relates to a novel process for obtaining a high contrastimage by treating with a lith type film developer a light-sensitivesilver halide photographic material, in which the amount of silverchloride contained in the emulsion layer is less than 30 mole percent ofthe total silver halide.

In the field of graphic arts, the advent of a photo graphic materialcapable of producing an extremely high contrast image and of a processfor treating the said photographic material is desired in order that ahigh dot quality or a hard line image can be obtained.

In order to meet the above demand, there has heretofore been efiected aprocess in which a lith type lightsensitive material is treated with ahigh contrast developer called a lith developer or an infectiousdeveloper. This developer is a hydroquinone-alkali developer having alow sulfite ion concentration and is prepared by use of formaldehydebisulfite, hydroquinone, alkali and potassium bromide, and the lith typelight-sensitive material is a photographic material containing at least50 mole percent of silver chloride. It is well known that an image whichis extremely high in contrast can be obtained when the saidlight-sensitive material is treated with the above mentioned lithdeveloper. A high speed type light-sensitive silver halide photographicmaterial containing such silver halide as silver bromide or silveriodobromide gives a low contrast image when treated with theconventional lith developer, and hence has not been used to obtain ahigh contrast image.

As the result of extensive studies, I have found an en tirely novel lithdeveloper which makes it possible to ob tain a high contrast image whenused'to treat the above mentioned high speed type light-sensitive silverhalide photographic material. Thus, the present invention provides anovel process for treating high speed type lightsensitive silver halidephotographic materials.

The light-sensitive silver halide photographic material used in thepresent invention is entirely different in com position of silver halidefrom the conventional lith type photographic material, and preferablycontains silver bromide or silver iodobromide. However, in case itcontains silver chloride, the amount of silver chloride should be lessthan 30 mole percent of the total amount of silver halide containedtherein. If the amount of silver chloride is more than 30 mole percent,fog is formed and no satisfactory image can be obtained.

Patented Mar. 26, 1974 The silver halide may be used in the form of amixed crystal or a mixture of individual crystals. In case multilayercoating is eifected, a same or different silver halide may beincorporated into individual layers.

For preparation of the photographic material used in the presentinvention, any of the known procedures may be adopted. For example, suchheavy metal ions as Cd++ or Pb++ may be made present at the time ofcrystal formation; such chemical sensitization as sulfur sensitization,gold sensitization or reduction sensitization may be effected, and suchadditives as film hardener, surfactant, stabilizer and high molecularbinder may be used.

The developer used in the present invention is prepared by entirelyremoving potassium bromide from the conventional alkali developercontaining hydroquinone as a sole developing agent, or removing thepotassium bromide to such an extent that the amount thereof becomes lessthan 0.004 mole per liter of the developer, and incorporating into thedeveloper a thiocyanate compound capable of liberating thiocyanate ion(SCN-). In case a developer containing Metol (N-methyl-p-aminophenolsulfate) and hydroquinone as developing agents is used, the resultingimage becomes low in contrast, and it is impossible to accomplish theobject of the present invention, i.e. the obtainment of a high contrastimage. The thiocyanate compound capable of liberating thiocyanate ionmay be any compound so far as it liberates thiocyanate ion (so far as itis photographically harmless). Typical examples of said compound includethiocyanic acid salts of alkali metals such as K and Na, divalent metalssuch as Ca, Mg and Ni, trivalent metals such as Cr, and ammonium. Theamount of the said compound to be added is not particularly limited, butfavorable results are obtained when the compound is added in an amountof less than 0.2 mole per liter of the developer used.

It is preferable that the developer contains no such bromide aspotassium bromide as far as possible. However, if such bromide is to bemade present in the developer, the amount thereof is desirably limitedto such a minute amount as less than 0.004 mole per liter of thedeveloper. In case the developer contains more than 0.004 mole of saidbromide, the resulting image becomes low in contrast. In additionthereto, the developer may contain substances used in the known lithdeveloper, e.g. a sulfite such as formaldehyde sulfite or sodiumsulfite, an alkali such as sodium carbonate or sodium hydroxide, a boroncompound such as borax or boric acid, and an antioxidant such asascorbic acid.

As mentioned above, the present invention is a process for developing ahigh speed type light-sensitive silver halide photographic material wtihan entirely novel lith developer, and this is a process capable ofobtaining a high contrast which has never been attained by use of a highspeed type light-sensitive silver halide photographic material.

The present invention is illustrated in further detail below withreference to examples.

EXAMPLE 1 Mixtures of alkali halides and silver nitrate were ripened at60 C. to prepare 4 kinds of emulsions having such silver halidecompositions as shown in Table l. The average particle size of eachsilver halide was made 0.5,u. The emulsions thus prepared wereindividually incorporated with sodium thiosulfate (sulfur sensitizer),subjected to chemical ripening, and then coated on a film base toprepare samples A, B, C and D.

TABLE 1 TABLE 5 Sample AgCl AgBr .AgI Developer A- 70 30 d e f B(present invention) 100 (present invention) 97 3 5 Sample S 'y F S 'Y FS 'Y F D (present invention) 90 A 1 7 0.01 3 8 0. 4 3 3 0.3 Nora-Thenumeral in Table 1 shows the mole percent of individual 0 5.5 2 0.01 107 0.02 9 6 0. 01

silver halides.

The samples A, B, C and D were individually exposed through a step wedgeand then developed at 20 C. for 2 /2 minutes with each of the 3developers shown in Table 2.

TABLE 2 Other Developer Stock solution G. additive Mole a Formaldehydebisulfite. 60 KBr 0.0168 b(present invention). Hydroquinone 18 KSCN0.0168 0 (present invention) Sodium carbonate 45 NH4SCN 0.02

Norm-The developers 1:, b, and c were individually prepared by addingeach of said other additives to the stock solution of the compositionshown in the table.

Subsequently, the samples thus developed were subjected to sensitometryto measure the relative speeds (S), gamma values and fog values (F) ofthe samples. The results obtained were as set forth in Table 3.

From Table 3, it is understood that when treated with the developer acontaining KBr which is a conventional developer, the sample A(conventional lith type photographic material) gives a high contrastimage, whereas the samples B, C and D (high speed photographic materialsused in the present invention) give low contrast images. On the otherhand, when treated with the developers b and c which are used in thepresent invention, the sample A is markedly increased in fog and gives ahalftone image, whereas the samples B, C and D are high in speed andless in fog and give high contrast images. The sample D contains 10 molepercent of silver chloride, and hence exhibits a greater increase in fogwhen treated with the developers d and 0, but is far less in fog thansamples B and C and gives a more high contrast image than the sample A.

EXAMPLE 2 The samples A and B prepared in Example 1 were individuallydeveloped at 20 C. for 2 /2 minutes with each of the developers d, e and1 shown in Table 4.

No'rE.The developers d, e and 1' were individually prepared by addingeatililoft other additives to the stock solution of the compositionshown in e a e.

Subsequently, the samples thus developed were subjected to sensitometryto obtain the results as set forth in Table 5.

Nora-In Table 5, S, 1 and F represent relative speeds, gamma values andfog values, respectively.

From Table 5, it is understood that when the photographic material Cused in the present invention is developed with the developer 1(containing a minute amount of KBr), the gamma value is far better thanin the case of the sample A.

What I claim is:

1. A process for obtaining a high contrast silver halide photographicimage, which comprises treating, after imagewise exposure to light, alight-sensitive silver halide photographic material having a silverhalide emulsion layer with a silver chloride content of less than 30mole percent of the total silver halide with a lith-type alkalideveloper containing hydroquinone as a developing agent, said developercontaining a thiocyanate compound capable of liberating thiocyanate ionand not more than 0.004 mole of potassium bromide per liter of thedeveloper.

2. A process for obtaining a high contrast silver halide photographicimage as claimed in claim 1, wherein said thiocyanate compound isselected from the group consisting of thiocyanates of potassium, sodium,calcium, magnesium, nickel and chromium and is added in an amount of notmore than 0.2 mole per liter of said alkali developer.

3. A process for obtaining a high contrast silver halide photographicimage as claimed in claim 1, wherein said alkali developer has thefollowing formulation:

G. Formaldehyde bisulfite 60 Hydroquinone 18 Sodium carbonate 45 Waterto make up 1 liter. KSCN 0.016'8 mole.

4. A process for obtaining a high contrast silver halide photographicimage as claimed in claim 1, wherein said alkali developer has thefollowing formulation:

G. Formaldehyde bisulfite 60 Hydroquinone 18 Sodium carbonate 45 Waterto make up 1 liter. NH SCN 0.02 mole.

5. A process for obtaining a high contrast silver halide photographicimage as claimed in claim 1, wherein said alkali developer has thefollowing formulation:

G. Sodium sulfite 30 'Paraformaldehyde 7.5 Sodium bisulfite 2.2 Boricacid 7.5 Hydroquinone 22.5 Potassium thiocyanate 1.6

Water to make up 1 liter.

6. A process for obtaining a high contrast silver halide photographicimage as claimed in claim 1, wherein said alkali developer has thefollowing formulation:

Water to make up 1 liter.

5 6 7. A process for obtaining a high contrast silver halide ReferencesCited photographic image, which comprises treating, after UNITED STATESPATENTS imagewise exposure to light, a light-sensitive silver halide3,695,883 10/1972 Yamamoto et ah photographic material having a silverhalide emulsion layer without silver chloride therein with a lith-typealkali 5 NORMAN TORCHIN, y Examiner developer comprising hydroquinone asa developing agent M. E. KELLEY, Assistant Examiner and a thiocyanatecompound capable of liberating thiocyanate ion and not more than 0.004mole of potassium 3 bromide per liter of the developer. 10

